Coexistence of silver and titanium dioxide nanoparticles: enhancing or reducing environmental risks?

Area of Science:

• Environmental Science
• Nanotechnology
• Ecotoxicology

Background:

• Silver nanoparticles (Ag NPs) and titanium dioxide nanoparticles (TiO2 NPs) possess bactericidal and photocatalytic properties, leading to widespread environmental and physiological applications.
• The combined presence of Ag NPs and TiO2 NPs in aquatic systems introduces uncertainties regarding their environmental fate and ecotoxicological impacts compared to individual nanoparticles.

Purpose of the Study:

• To investigate the ecotoxicological risks associated with the co-existence of TiO2 NPs and Ag NPs in aquatic environments.
• To assess the influence of different illumination conditions on the behavior and toxicity of Ag NPs in the presence of TiO2 NPs, using ciliated protozoa (Tetrahymena pyriformis) as a model organism.

Main Methods:

• Monitoring of silver ion (Ag+) release, physicochemical properties, and oxidative stress biomarkers in Tetrahymena pyriformis exposed to Ag NPs and TiO2 NPs under varying light conditions (dark, natural light, continuous illumination).
• Toxicity testing to evaluate the effects of TiO2 NPs on Ag NP toxicity under different illumination modes.
• Analysis of silver ion adsorption onto TiO2 NPs surfaces and the formation of TiO2-Ag NPs complexes.

Main Results:

• Continuous illumination decreased Ag+ release from Ag NPs by 20.0% compared to dark conditions.
• TiO2 NPs reduced Ag+ concentration by 64.3% under continuous illumination compared to Ag NPs alone.
• The toxicity of Ag NPs was modulated by TiO2 NPs differently under various light conditions: no effect in dark, antagonism in natural light (reducing toxicity by 28.7%), and synergism in continuous light (increasing toxicity by 6.93%).
• Continuous light exposure significantly increased SOD activity in the control group (1.96 times).
• TiO2 NPs reduced CAT activity by an average of 36.1% under light exposure.

Conclusions:

• TiO2 NPs reduce the environmental risks of Ag NPs in natural light primarily through Ag+ adsorption onto TiO2 NP surfaces.
• Under continuous illumination, TiO2 NPs can enhance the environmental risks of Ag NPs by forming activated TiO2-Ag NPs complexes.
• The illumination mode significantly alters the surface chemistry of Ag NPs in the presence of TiO2 NPs, leading to varied ecotoxicological outcomes.